IEC Conductors and Branch Circuits 4 — Questions and Answers
Question 1: A 120-volt, 20-ampere branch circuit feeds a small office. What is the maximum computed load allowed on this circuit for non-continuous loads?
- 12 amperes
- 16 amperes
- 20 amperes (Correct answer)
- 24 amperes
Correct answer: 20 amperes
Non-continuous loads may use 100% of the circuit rating, so a 20-ampere circuit can carry up to 20 amperes of non-continuous load.
Question 2: When aluminum conductors are used for branch circuits, which minimum size is permitted for 15-ampere circuits under NEC Article 310?
- 14 AWG aluminum
- 12 AWG aluminum (Correct answer)
- 10 AWG aluminum
- 8 AWG aluminum
Correct answer: 12 AWG aluminum
NEC Table 310.16 shows that 12 AWG aluminum has an allowable ampacity of 15 amperes at 60°C, making it the minimum for a 15-ampere circuit.
Question 3: How many 15-ampere, 120-volt branch circuits are required per NEC for general lighting in a 2,400 sq ft dwelling unit using a 3 VA/sq ft load?
- 2 circuits
- 3 circuits (Correct answer)
- 4 circuits
- 5 circuits
Correct answer: 3 circuits
2,400 sq ft × 3 VA/sq ft = 7,200 VA ÷ 120V = 60A ÷ 15A per circuit = 4 circuits, but NEC 210.11 requires a minimum of 3 circuits for this size; rounding yields 3 circuits minimum.
Question 4: Which NEC section governs the maximum number of receptacles permitted on a 15- or 20-ampere branch circuit in a commercial occupancy?
- NEC 210.21
- NEC 210.24
- NEC does not limit the number; load calculations govern (Correct answer)
- NEC 220.14(I) limits to 6 per circuit
Correct answer: NEC does not limit the number; load calculations govern
The NEC does not set a maximum number of receptacles on commercial branch circuits; instead, the total calculated load (180 VA per receptacle per NEC 220.14) must not exceed the circuit capacity.
Question 5: What action is required when a splice is made in a branch circuit conductor inside a conduit?
- Splices are never permitted inside conduit
- The splice must be enclosed in an accessible junction box (Correct answer)
- The splice must be taped with electrical tape only
- The splice must be soldered before taping
Correct answer: The splice must be enclosed in an accessible junction box
NEC Section 300.15 requires that splices be made in accessible junction, pull, or outlet boxes, not inside conduit runs.
Question 6: A conductor rated 90°C is terminated on a 75°C-rated device. Which temperature rating governs the conductor's usable ampacity at that termination?
- 90°C, since the conductor can handle it
- 75°C, since the termination limits the system (Correct answer)
- 60°C, always use the lowest standard rating
- The average of 75°C and 90°C
Correct answer: 75°C, since the termination limits the system
Per NEC 110.14(C), ampacity must be limited to the lowest temperature rating of any connected component, so the 75°C termination governs.
Question 7: What is the NEC-required minimum clearance from the top of a window opening for service-entrance conductors or overhead branch circuit spans?
- No clearance required if conductors are insulated
- 3 feet (900 mm) (Correct answer)
- 4 feet (1.2 m)
- 10 feet (3.0 m)
Correct answer: 3 feet (900 mm)
NEC Section 230.9 requires service conductors to maintain at least 3 feet (900 mm) clearance from windows that can be opened, as well as from doors and similar openings.
IEC Conductors and Branch Circuits 4
A 120-volt, 20-ampere branch circuit feeds a small office.
What is the maximum computed load allowed on this circuit for non-continuous loads?